263 Prof. S. F. Baird on the Distribution and 



specimens in the museum of the Smithsonian Institution, I may 

 say that, as far as its ornithology, and, to a considerable degree, 

 its vertebrate zoology in general, is concerned, North America 

 appears to be divided into two great regions, an eastern and a 

 western, which in the United States are of approximately equal 

 extent, but very unequal further north. The eastern ■ division 

 extends from the Atlantic seaboard, westward across the Alle- 

 ghanies (which affect the distribution of species but little) and 

 over the valley of the Mississippi and its fertile prairies to about 

 the 100th degree of longitude, or to the beginning of the sterile 

 plains. Its western border is not sharply defined, nor strictly 

 in a meridian line, but somewhat oblique, and interdigitates 

 with the western division by extending westward along the 

 river-bottoms, some species, as Galeoscojytes carolinensis, Vireo 

 olivaceus, &c., occurring as far v/est as Fort Benton, or even Fort 

 Colville. 



The western division begins at the western border of the 

 eastern,oralong the sterile plains of the trans-Mississippi country, 

 and extends across to the Pacific Ocean. The character of the 

 ornithological fauna of this division is much the same through 

 and beyond the Rocky Mountains to the eastern slope of the 

 Sierra Nevada and Cascade Mountains of California and Oregon, 

 but changes somewhat on the western slope and thence to the 

 Pacific, and, although to a considerable extent uniform, yet 

 exhibits some modifications which may warrant a separation 

 into a western and middle division, making three in all, which 

 we may call provinces, of very unequal extent, and exhibiting 

 further modifications or subdivisions with latitude, as I shall 

 proceed to explain, taking into consideration the whole conti- 

 nent north of Mexico. 



As previously remarked, the eastern province or division 

 extends from the Atlantic Ocean to about the meridian of 100° 

 west from Greenwich, or 23° west from Washington. The line 

 of division on the Gulf of Mexico starts near the eastern border 

 of Texas, perhaps between the Brazos and the Sabine, and, fol- 

 lowing up the direction of the former river to the approaches of 

 the Great Desert nearly on the meridian mentioned, proceeds 

 northward, forced sometimes more or less westward, especially 



